File: Caltrain arrives at the train station next to the Box, Inc. headquarters office building in Redwood City, Calif. on Wednesday, April 19, 2017.

Photo: Paul Chinn / The Chronicle

A Caltrain traveling southbound fatally struck a woman on the tracks in Redwood City on Wednesday, transportation officials said.

The involved train, SB156, struck a woman who was on the tracks around 4 p.m. at the Main Street Grade Crossing in Redwood City, said Tasha Bartholomew, a spokeswoman for the San Mateo County Transit District, which oversees Caltrain, SamTrans and the San Mateo County Transportation Authority.

The woman, who was not identified pending family notification, is Caltrain’s 11th fatality in 2018, Bartholomew said.

Roughly 454 passengers were aboard at the time. No additional injuries were reported.

Officials with San Mateo County Sheriff’s Transit Police Bureau, that patrols the Caltrain region, are investigating the incident.

While Bartholomew said the San Mateo County Coroner’s office determines the cause and manner of death, she said officials believe the incident appears to have been an “intentional act.”

“No matter what the circumstances, it is always regrettable when a life is lost,” she said in a statement. “Caltrain reminds everyone to be safe around train tracks.”

At 4:33 p.m. on Wednesday, transit officials opened the northbound track for single-tracking at restricted speeds through the area immediately surrounding the area.

The coroner’s office and transit police arrived soon after to scour the scene for evidence, officials said.

The southbound track is estimated to reopen around 7 p.m. on Wednesday.

Riders were delayed for up to an hour in both the northbound and southbound directions on Wednesday.

Unfortunately that train is now part of an investigation. We will move the train as soon as we can safely do so. Our first responders are working around the train at this moment. We appreciate your patience.

Lauren Hernández joined The San Francisco Chronicle in 2018. She covers crime, mayhem and breaking news. Previously, she was a breaking news reporter for the USA TODAY Network’s Statesman Journal in Salem, Oregon. She graduated from San Jose State University in 2015 with a bachelor’s of science in journalism and a minor in philosophy. She is a member of the National Association of Hispanic Journalists. She is also a licensed drone pilot through the Federal Aviation Administration.